Mo. Rev. Stat. § 478.270: Judge or clerk not to prepare wills or settlements — letters revoked, when.

1. No judge or clerk of the probate division of the circuit court shall draw or witness any will or make any settlement for any administrator, executor or guardian over which his court has jurisdiction.

2. The acceptance of the office of judge of the probate division of the circuit court operates as a revocation of all letters testamentary and of administration and of guardianship held by a judge of a probate division of a circuit court at the time of his election, and disqualifies him from acting in any capacity in such cases in any court of this state.